DC motors may be provided with means to prevent or diminish an initial torque spike caused by an inrush current associated with starting, in order to avoid damage to the DC motors or to any mechanical load coupled to the DC motors. Various solutions for such “soft starting” of DC motors are known. For example, one solution includes limiting the inrush current to the armature of a DC motor by connecting a variable resistance in series with the armature. Another solution includes disconnecting any mechanical load from the output shaft of the DC motor during starting and later reconnecting the load. For aircraft applications, these solutions may be cumbersome, heavy and therefore undesirable. For example, a DC motor serving as a starter motor for a gas turbine engine may experience an inrush current of around 1200 to 1500 amperes. Equipment required to limit inrush current of such magnitude may be heavy and not sufficiently reliable for an aircraft application. Similarly, decoupling of a mechanical load from the output shaft during starting may require the use of a clutch that may be heavy and prone to wear and failure.
Improvement in starting of DC motors is therefore desirable.